1. Field of the Invention
The present invention relates to a charge/discharge protection apparatus provided in a battery pack that supplies power to a mobile electronic system, the charge/discharge protection circuit protecting a secondary battery, such as a lithium-ion battery, from being damaged when the battery is placed in an overcharge condition, an over-discharge condition, a discharge-state overcurrent condition or a charge-state overcurrent condition. Further, the present invention relates to a battery pack in which the secondary battery and the charge/discharge protection circuit are provided.
2. Description of the Related Art
In recent mobile electronic systems, a battery pack containing a secondary or rechargeable battery, such as a lithium-ion battery, is often used as the power supply that supplies power to the mobile electronic system. When the time the lithium-ion battery continues to be in overcharge condition is excessively long, the deposition of lithium metal will occur, which damages the battery pack or the mobile electronic system. On the other hand, when the time the lithium-ion battery continues to be in an over-discharge condition is excessively long, the repetitive charge/discharge operational life of the battery pack will deteriorate.
Conventionally, in order to eliminate the problems, a protection switch is provided on the charge/discharge current line between the secondary battery and the electronic system body. The protection switch is turned off when the overcharge condition or the over-discharge condition of the battery is detected, so as to disconnect the secondary battery from the charge/discharge current line. By using the protection switch, it is possible to avoid the continuation of the overcharge condition of the over-discharge condition of the secondary battery.
For example, Japanese Laid-Open Patent Application No. 11-103528 discloses a charge/discharge protection circuit for protecting a secondary battery from damage, which detects an overcharge condition, an over-discharge condition or a discharge-state overcurrent condition of the battery. In the protection circuit of the above document, the terminal to which the voltage of the battery is applied is constructed in a low voltage-resistance structure, and only the terminal to which the voltage of the charger (part of the semiconductor device) is applied is constructed in a high voltage-resistance structure. Such configuration allows the high voltage-resistance structure of the entire protection circuit, and it is possible to safely prevent the damaging of the protection circuit even when an improper charger is erroneously attached to supply a high voltage to the secondary battery.
The conventional protection circuit of the above document is capable of detecting the discharge-state overcurrent condition only. However, the conventional protection circuit of the type is not provided with a function of detecting a charge-state overcurrent condition of the battery. In order to protect the damaging of the secondary battery in the charge state after an improper charger (a defective or broken charger) is attached to the battery pack, the conventional protection circuit requires an externally attached fuse or the like. For this purpose, the conventional protection circuit including a mounting portion for the externally attached fuse has to be large in size, and the manufacturing cost will be raised.
Further, Japanese Laid-Open Patent Application No. 9-182283 discloses a charge/discharge protection circuit which detects any of an overcharge condition, an over-discharge condition and a discharge-state overcurrent condition of a lithium-ion battery. FIG. 7 shows a conventional charge/discharge protection circuit which is disclosed in the above document.
Generally, when the battery voltage is nearly equal to an operation stop voltage at which the discharging operation should be stopped, the voltage margin becomes small and a malfunction in the protection circuit due to a rapid change of the loading voltage is likely to occur. The setting of the protection switch in OFF state immediately after the battery voltage is equal to the operation stop voltage is avoided. It is desirable to set the protection switch in OFF state only when it is determined that the time the secondary battery is continuously set in any of the overcharge condition, the over-discharge condition and the discharge-state overcurrent condition exceeds a given reference period. To detect any of the overcharge condition, the over-discharge condition and the discharge-state overcurrent condition of the secondary battery, the conventional charge/discharge protection circuit in FIG. 7 utilizes a timer including an internal oscillator and a frequency-division counter.
As shown in FIG. 7, the conventional charge/discharge protection circuit is formed on an integrated circuit (IC) chip, and it generally includes an internal oscillator (OSC) 501, a frequency-division counter (FDC) 502, an OR gate 503, a voltage comparator (COMP) 504, a decoder (DEC) 505, an inverter 506, a protection switch 507, and a latch (LTC) 508.
In the conventional charge/discharge protection circuit of FIG. 7, the voltage comparator 504 compares a divided battery voltage VCC/N with a given reference voltage V4. When the battery voltage VCC is detected as being less than the operation stop voltage, the voltage comparator 504 outputs a low-level detection signal to the counter 502. At this time, the resetting of the counter 502 to zero is canceled by the low-level detection signal, so that the counter 502 starts counting. When the count value obtained at the counter 502 reaches a predetermined value that is set to the decoder 505, the decoder 505 sets the latch 508 so as to set the protection switch 507 in OFF state. The protection switch 507 is constructed by a MOS (metal-oxide semiconductor) transistor.
However, when the battery voltage is raised to a level higher than the operation stop voltage before the count value reaches the predetermined value, the voltage comparator 504 outputs a high-level detection signal (reset signal) to the counter 502. At this time, the counting of the counter 502 is canceled by the reset signal, so that the count value thereof is reset to zero. If the predetermined value that is set to the decoder 505 is made to a comparatively large value, it is possible to prevent the erroneous operation of the protection switch 507 even when the battery voltage VCC is temporarily changed to the level below the operation stop voltage due to a change of the loading voltage.
The above operation of the conventional protection circuit is given for explaining the detection of the over-discharge condition. Similar to the detection of the over-discharge condition, the delay time upon detection of the overcharge condition or the discharge-state overcurrent condition can be controlled by using the internal oscillator 501 and the counter 502 in the conventional protection circuit. Conventionally, in order to determine the delay times upon detection of these conditions, an externally attached capacitor has been needed on the protection circuit IC. According to the above-described conventional protection circuit of FIG. 7, the externally attached capacitor is no longer needed, and it is possible to reduce the total number of circuit components needed for the protection circuit.
The conventional protection circuit of FIG. 7 is not provided with a function of detecting a charge-state overcurrent condition of the battery. In order to protect the damaging of the battery in the charge state after an improper charger is attached to the battery pack, the conventional protection circuit requires an externally attached fuse or the like.
Further, the delay time upon detection of the over-discharge condition or the discharge-state overcurrent condition of the battery is usually set to a time on the order of 10 to 102 ms. However, the delay time when detecting the overcharge condition of the battery is usually set to a time on the order of several 103 ms. In the conventional protection circuit disclosed in the above document (JP 9-182283), it is difficult to shorten the testing time when performing an operation test of the conventional protection circuit that requires accurate measurement of the detection voltage with respect to the overcharge condition.
An object of the present invention is to provide an improved charge/discharge protection apparatus in which the above-described problems are eliminated.
Another object of the present invention is to provide a charge/discharge protection apparatus which is capable of detecting a charge-state overcurrent condition of a secondary battery, and safely and reliably protects the battery against the charge-state overcurrent condition with no need for an externally attached fuse, by eliminating the charge-state overcurrent condition of the battery in an appropriate manner.
Another object of the present invention is to provide a charge/discharge protection apparatus which can shorten the testing time when conducting an operation test of the charge/discharge protection apparatus that requires accurate measurement of the detection voltage with respect to the overcharge condition.
Another object of the present invention is to provide a battery pack which includes a secondary battery and a charge/discharge protection apparatus, the charge/discharge protection apparatus having a capability to detect a charge-state overcurrent condition of a secondary battery, and safely and reliably protecting the battery against the charge-state overcurrent condition, with no need for an externally attached fuse, by eliminating the charge-state overcurrent condition of the battery in an appropriate manner.
The above-mentioned objects of the present invention are achieved by a charge/discharge protection apparatus for protecting a secondary battery of a battery pack from damage, the charge/discharge protection apparatus comprising: a switch which is provided on a charge/discharge current line, the charge/discharge current line being connected to the battery; a charge-state overcurrent detector outputting a control signal when a charge-state overcurrent condition of the battery is detected in a charge state of the battery pack; and a control unit which sets the switch in OFF state to cut off connection between the charge/discharge current line and the battery in response to the control signal output by the charge-state overcurrent detector.
The above-mentioned objects of the present invention are achieved by a battery pack including a secondary battery and a charge/discharge protection apparatus, the charge/discharge protection apparatus comprising: a switch which is provided on a charge/discharge current line, the charge/discharge current line being connected to the battery; a charge-state overcurrent detector outputting a control signal when a charge-state overcurrent condition of the battery is detected in a charge state of the battery pack; and a control unit which sets the switch in OFF state to cut off connection between the charge/discharge current line and the battery in response to the control signal output by the charge-state overcurrent detector.
In the charge/discharge protection apparatus of one preferred embodiment of the invention, when any of the overcurrent condition, the over-discharge condition, the discharge-state overcurrent condition, the short-circuit condition or the charge-state overcurrent condition is detected by the corresponding detector, the corresponding detector outputs a control signal to an oscillator circuit. The oscillator circuit starts outputting of a clock signal to a counter circuit. The output of the oscillator circuit is connected to the input of the counter circuit. The counter circuit starts counting of the clock signals received from the oscillator circuit. When the count value obtained at the counter circuit reaches a predetermined delay time, the control unit sets the switch in OFF state. In other words, when the delay time is reached after the detection of the undesired condition, the control unit sets the switch in OFF state. Since the charge/discharge current line to which the secondary battery is connected is cut off at the switch in the undesired condition, the charge/discharge protection apparatus protects the secondary battery from damage.
Therefore, the charge/discharge protection apparatus of the present invention is capable of detecting a charge-state overcurrent condition of the battery with no need for an externally attached fuse, and is effective in safely and reliably protecting the battery against the charge-state overcurrent by eliminating the charge-state overcurrent condition. There is no need for an externally attached fuse or the like to protect the battery against the charge-state overcurrent condition, and the manufacturing cost can be reduced.
In the charge/discharge protection apparatus of one preferred embodiment of the invention, a delay circuit, a test terminal, a test-mode switch and a delay time reducing unit are provided to reduce the entire period of a testing time of the charge/discharge protection apparatus. It is possible for the charge/discharge protection apparatus of the preferred embodiment to shorten the entire period of the testing time when performing an operation test of the charge/discharge protection apparatus that requires accurate measurement of the detection voltage with respect to the overcharge condition of the battery.